Battery diaphragm and preparation method thereof, thermal composite battery cell and secondary battery

Abstract

The invention discloses a battery diaphragm and a preparation method thereof, a thermal composite battery cell and a secondary battery, and belongs to the field of secondary batteries, the battery diaphragm comprises a carrier layer and matrix type adhesive layers stacked on the surfaces of the two sides of the carrier layer, and the matrix type adhesive layers comprise a plurality of adhesive points which are distributed in a matrix and are arranged in a raised manner. The adhesive point is prepared from the following components in parts by mass: 8 to 16 parts of polymer, 2 to 7 parts of binder, 0.5 to 1.5 parts of dispersing agent, 3 to 9 parts of thickening agent and 0.1 to 0.4 part of wetting agent; the glass transition temperature of the polymer is-50 DEG C to 100 DEG C, and the particle size D50 of the polymer is 0.5 mu m to 50 mu m. By arranging the matrix type adhesive layer and improving the composition of the matrix type adhesive layer, the adhesion and liquid retention performance of the battery diaphragm can be enhanced, and the ventilation increment of the diaphragm is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a battery separator and a preparation method thereof, a thermal composite battery cell, and a secondary battery. Background Art

[0002] In secondary batteries, battery separators primarily serve to separate the positive and negative electrodes and allow ions to pass freely. Currently, it is hoped that battery separators can bond with both the positive and negative electrode sheets to inhibit movement during expansion, thereby improving the interfacial properties of the battery sheets and increasing the battery's cycle life.

[0003] In related art, battery separators include a base film and an adhesive layer applied to the surface of the base film. The adhesive layer includes a polymer, a binder, a wetting agent, and the like, which acts as an adhesive. The adhesive layer can be applied to the surface of the base film by a full coating. However, this type of battery separator suffers from poor polymer uniformity in the adhesive layer, resulting in poor adhesion. This also tends to result in a large increase in the air permeability of the battery separator, and the electrolyte absorption and retention properties need to be improved. Summary of the Invention

[0004] In view of this, the present invention provides a battery separator and its preparation method, a thermal composite battery cell, and a secondary battery, which can solve the problems of poor adhesion, large air permeability, and improved liquid absorption and retention of battery separators in related technologies. Specifically, it includes the following technical solutions:

[0005] On the one hand, a battery separator is provided, which includes: a carrier layer and a matrix adhesive layer stacked on the two side surfaces of the carrier layer, the matrix adhesive layer including a plurality of glue dots distributed in a matrix and arranged in a raised manner; the glue dots include the following components in parts by mass: 8-16 parts of polymer, 2-7 parts of binder, 0.5-1.5 parts of dispersant, 3-9 parts of thickener, and 0.1-0.4 parts of wetting agent; the glass transition temperature of the polymer is -50°C to 110°C, and the particle size D50 of the polymer is 0.5μm-50μm.

[0006] In some possible implementations, the polymer is selected from at least one of polyvinylidene fluoride, hexafluoropropylene-modified polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyethylene-co-vinyl acetate, polyimide, and polyethylene oxide.

[0007] In some possible implementations, the binder is selected from at least one of polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, silicone-modified polyacrylate, polyurethane-modified polyacrylate, and methacryloyl epoxy ester.

[0008] In some possible implementations, the dispersant is selected from at least one of sodium hexametaphosphate, triethyl phosphate, sodium polyacrylate, ammonium polyacrylate, polyethylene glycol, polyvinyl alcohol, naphthalenesulfonic acid condensate, sodium cellulose sulfonate, and sodium lignin sulfonate.

[0009] In some possible implementations, the thickener is selected from at least one of sodium hydroxymethyl cellulose and xanthan gum.

[0010] In some possible implementations, the wetting agent is selected from at least one of a polyether wetting agent, a silicone and polyether mixture wetting agent, and an alcohol alkoxylate wetting agent.

[0011] In some possible implementations, the maximum radial dimension of the glue dots in a direction parallel to the carrier layer is 50 μm-1200 μm, the height of the glue dots is 0.5 μm-10 μm, and the center distance between any two adjacent glue dots is 300 μm-1200 μm.

[0012] In some possible implementations, the amount of the matrix adhesive layer applied on the surface of the carrier layer is 0.3 g / m 2 -1.5g / m 2 The coverage rate of the matrix adhesive layer on the surface of the carrier layer is 20%-80%.

[0013] In some possible implementations, the carrier layer includes a base film, and the base film is a polyethylene base film or a polypropylene base film.

[0014] In some possible implementations, the base film satisfies at least one of the following parameters: a molecular weight of 300,000 g / mol-3,000,000 g / mol; a thickness of 1 μm-30 μm; and an air permeability of 50 s / 100 ml-500 s / 100 ml.

[0015] In some possible implementations, the projected shape of the plurality of glue dots on a plane parallel to the carrier layer includes at least one of a circle, an ellipse, a square, and a polygon.

[0016] On the other hand, a method for preparing a battery separator is provided. The battery separator is as described above, and the preparation method includes: providing a slurry, the slurry including a glue layer composition and water for forming a matrix glue layer; using a matrix coating process to apply the slurry on both side surfaces of the carrier layer, and after curing treatment, forming a matrix glue layer on both side surfaces of the carrier layer to prepare the battery separator.

[0017] On the other hand, a thermal composite battery cell is provided, which includes multiple positive electrode sheets, multiple negative electrode sheets, and any of the above-mentioned battery separators; the negative electrode sheets and the positive electrode sheets are alternately stacked, and the adjacent negative electrode sheets and the positive electrode sheets are separated by the battery separator, and the battery separator is respectively bonded to the positive electrode sheets and the negative electrode sheets through matrix adhesive layers on both sides.

[0018] In another aspect, a secondary battery is provided, comprising: a shell, an electrolyte contained in the shell, and a thermal composite battery cell, wherein the thermal composite battery cell is as described above.

[0019] The beneficial effects of the technical solution provided by the embodiment of the present invention include at least:

[0020] The battery separator provided by embodiments of the present invention, on the one hand, comprises a matrix adhesive layer disposed on the surface of a carrier layer. The matrix adhesive layer comprises a plurality of adhesive dots arranged in a matrix and in a raised configuration. The uniform distribution of the multiple adhesive dots enhances the adhesiveness of the matrix adhesive layer, and the raised configuration of the multiple adhesive dots increases the contact area with the carrier layer and the electrode. This not only enhances the adhesiveness of the battery separator but also facilitates the formation of a gap between the battery separator and the electrode, thereby improving the battery separator's ability to absorb and retain electrolyte. The discrete design of the multiple adhesive dots, which only partially covers the carrier layer, also helps reduce the incremental air permeability of the battery separator. Furthermore, the composition of the adhesive dots in the matrix adhesive layer is improved. The polymer transitions from a glassy state to a highly elastic state at temperatures above its glass transition temperature, allowing the polymer to perform its adhesive function even when heated. The polymer is in the form of a micron-sized powder, facilitating its uniform distribution within the matrix adhesive layer and promoting uniform adhesion of the adhesive dots. By adding specific amounts of binders, dispersants, thickeners and wetting agents to the glue dots, the various components work synergistically. The binder works with the polymer to further enhance the adhesion of the matrix glue layer. The dispersant can effectively inhibit polymer agglomeration. The wetting agent helps to reduce the surface energy of the glue dots and promotes capillary filling of the electrolyte. The thickener works with the polymer to form a cross-linked network to accommodate the electrolyte. The above is beneficial for enhancing the adhesion and liquid retention performance of the matrix glue layer and reducing the air permeability increase of the battery separator. DETAILED DESCRIPTION

[0021] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0022] An embodiment of the present invention provides a battery separator comprising: a carrier layer and a matrix adhesive layer stacked on both sides of the carrier layer, the matrix adhesive layer comprising a plurality of adhesive dots arranged in a matrix and raised. It should be noted that the adhesive dots are arranged raised relative to the surface of the carrier layer, and the matrix shape formed by the plurality of adhesive dots includes, but is not limited to, a square matrix, a rectangular matrix, a diamond matrix, and a regular polygonal matrix with more than four sides, such as a regular hexagonal matrix.

[0023] The glue dots include the following components by weight: 8-16 parts polymer, 2-7 parts binder, 0.5-1.5 parts dispersant, 3-9 parts thickener, and 0.1-0.4 parts wetting agent. The polymer has a glass transition temperature of -50°C to 100°C and a particle size (D50) of 0.5-50 μm.

[0024] The battery separator provided by embodiments of the present invention, on the one hand, comprises a matrix adhesive layer disposed on the surface of a carrier layer. The matrix adhesive layer comprises a plurality of adhesive dots arranged in a matrix and in a raised configuration. The uniform distribution of the multiple adhesive dots enhances the adhesiveness of the matrix adhesive layer, and the raised configuration of the multiple adhesive dots increases the contact area with the carrier layer and the electrode. This not only enhances the adhesiveness of the battery separator but also facilitates the formation of a gap between the battery separator and the electrode, thereby improving the battery separator's ability to absorb and retain electrolyte. The discrete design of the multiple adhesive dots, which only partially covers the carrier layer, also helps reduce the incremental air permeability of the battery separator. Furthermore, the composition of the adhesive dots in the matrix adhesive layer is improved. The polymer transitions from a glassy state to a highly elastic state at temperatures above its glass transition temperature, allowing the polymer to perform its adhesive function even when heated. The polymer is in the form of a micron-sized powder, facilitating its uniform distribution within the matrix adhesive layer and promoting uniform adhesion of the adhesive dots. By adding specific amounts of binders, dispersants, thickeners and wetting agents to the glue dots, the various components work synergistically. The binder works with the polymer to further enhance the adhesion of the matrix glue layer. The dispersant can effectively inhibit polymer agglomeration. The wetting agent helps to reduce the surface energy of the glue dots and promotes capillary filling of the electrolyte. The thickener works with the polymer to form a cross-linked network to accommodate the electrolyte. The above is beneficial for enhancing the adhesion and liquid retention performance of the matrix glue layer and reducing the air permeability increase of the battery separator.

[0025] The polymer is used in the matrix adhesive layer to form the main body of the adhesive dot and provide suitable adhesion and mechanical strength. For the polymer, its mass proportion in the adhesive dot can be any of the following values ​​or an interval consisting of two of the following values: 8 parts, 8.5 parts, 9 parts, 9.5 parts, 10 parts, 10.5 parts, 11 parts, 11.5 parts, 12 parts, 12.5 parts, 13 parts, 13.5 parts, 14 parts, 14.5 parts, 15 parts, 15.5 parts, 16 parts, etc.

[0026] The particle size D50 of the polymer is 0.5μm-50μm, and can further be 1μm-30μm, and further can be 5μm-20μm, etc. For example, the particle size D50 of the polymer can be any of the following point values ​​or an interval composed of any two of the following point values: 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, etc. By limiting the powder particle size of the polymer as above, on the one hand, it is beneficial to the uniform distribution of the polymer in the glue dots, and on the other hand, it is beneficial to accurately control the morphology of the glue dots.

[0027] The glass transition temperature T of the polymer g The temperature range is -50°C to 110°C. In other words, the premise for the polymer to achieve adhesion is that the temperature is at least greater than its glass transition temperature. Furthermore, the polymer melts into a viscous flow state at a temperature greater than its viscous flow temperature, thereby achieving melt bonding. Some polymers that meet this requirement can be selected from at least one of polyvinylidene fluoride (PVDF), hexafluoropropylene-modified polyvinylidene fluoride (PVDF-HPF), polymethyl methacrylate (PMMA), polyacrylonitrile, polyvinyl acetate, polyethylene-co-vinyl acetate, polyimide, and polyethylene oxide.

[0028] The polymer is polar or contains polar groups, which is not only conducive to enhancing the bonding effect of the matrix adhesive layer, but also conducive to improving the wettability of the matrix adhesive layer with the electrolyte and improving its liquid absorption and retention rate.

[0029] For further example, the polymer is selected from at least one of polyvinylidene fluoride (PVDF), hexafluoropropylene-modified polyvinylidene fluoride (PVDF-HPF), and polymethyl methacrylate (PMMA).

[0030] Polyvinylidene fluoride (PVDF) can bind to polar sites on the surface of a carrier layer (such as a PP-based membrane or a PE-based membrane) due to its polar groups, significantly improving the interfacial bonding between the adhesive layer and the carrier layer. The polar groups of PVDF have a strong affinity for carbonate electrolytes, which improves the liquid absorption rate of the adhesive layer. In addition, PVDF has strong thermal stability and maintains its structural integrity when the battery is overcharged (above 120°C), preventing uncontrolled ventilation caused by melting of the adhesive layer.

[0031] Hexafluoropropylene-modified polyvinylidene fluoride (PVDF-HPF), based on the introduction of hexafluoroisopropyl, helps improve the elongation at break of the adhesive layer, adapt to the volume deformation during battery charging and discharging, and reduce the problem of cracking in the adhesive points. Moreover, the increase in the amorphous region promotes the formation of electrolyte infiltration channels, improves the internal porosity of the matrix adhesive points, and makes the pore size distribution more uniform, thereby ensuring ion conduction while inhibiting lithium dendrite penetration. In addition, the melting temperature of hexafluoropropylene-modified polyvinylidene fluoride is lower than that of polyvinylidene fluoride, making it more process-friendly.

[0032] Polymethyl methacrylate (PMMA), based on its polar groups, gives the adhesive layer good adhesion. In addition, its ester group has a strong ability to solvate Li+, the adhesive layer has high conductivity, and it can also fix the electrolyte through the hydrogen bond network to achieve the purpose of improving the liquid absorption rate.

[0033] For the adhesive, its mass proportion in the glue dot can be any of the following values ​​or an interval consisting of two of the values: 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, 5.5 parts, 6 parts, 6.5 parts, 7 parts, etc.

[0034] In some examples, the adhesive is an acrylic adhesive, which can be selected from at least one of polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, silicone-modified polyacrylate, polyurethane-modified polyacrylate, and methacryloyl epoxy ester.

[0035] The above-mentioned adhesive can not only further enhance the adhesive force of the matrix adhesive layer (for example, achieving stable bonding with the carrier layer and the polymer through the carboxylic acid group), but also facilitates the formation of an elastic network to inhibit deformation and cracking of the adhesive layer.

[0036] In addition, the above-mentioned acrylic binder has a significant regulatory effect on the process of polymer primary particles (i.e., single polymer powder particles) agglomerating into secondary particles (i.e., agglomerate particles formed by the agglomeration of multiple primary particles). It converts the random agglomeration of polymer primary particles into controllable, high-strength, and functionalized secondary particles through the triple effects of dispersion regulation (anti-agglomeration), interface bridging (strong structure), and gradient function (excellent performance). It can not only solve the problem of "easy to break and uneven porosity" of traditional agglomerates, but also the carboxyl active groups of the binder give the secondary particles complex functions such as interface bonding, ion conduction, and liquid retention and locking, thereby improving the cycle life of the diaphragm.

[0037] The dispersant serves to disperse the glue points and prevent the glue points from agglomerating. Its mass content in the glue points can be any of the following values ​​or an interval consisting of two of them: 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts, etc.

[0038] For example, some suitable dispersants are selected from at least one of sodium hexametaphosphate, triethyl phosphate, sodium polyacrylate, ammonium polyacrylate, polyethylene glycol, polyvinyl alcohol, naphthalenesulfonic acid condensate, sodium cellulose sulfonate, and sodium lignin sulfonate. These dispersants can synergize with other components in the adhesive to achieve a good dispersion effect.

[0039] The thickener forms a cross-linked network in the adhesive dot after curing, maintaining the adhesive dot's structural shape. This contributes to the membrane's liquid retention and air permeability. The thickener content by weight in the adhesive dot can be any of the following values, or a range of two of these values: 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, 5.5 parts, 6 parts, 6.5 parts, 7 parts, 7.5 parts, 8 parts, 8.5 parts, 9 parts, etc.

[0040] Some suitable thickeners are selected from at least one of sodium hydroxymethyl cellulose (NaCMC) and xanthan gum, for example, sodium hydroxymethyl cellulose. When preparing the glue dots, the sodium hydroxymethyl cellulose can be pre-mixed with water to form a sodium hydroxymethyl cellulose glue solution with a mass concentration of 0.5% to 1%. Subsequently, the sodium hydroxymethyl cellulose glue solution and other components are dissolved in water to form a slurry.

[0041] Wetting agents can reduce the surface tension of the adhesive dot, ensuring wettability between the matrix adhesive layer, the carrier layer, and the electrode, which is beneficial for improving the adhesion of the diaphragm. The mass percentage of wetting agent in the adhesive dot can be any of the following values ​​or a range of two of these values: 0.1 part, 0.15 part, 0.2 part, 0.25 part, 0.3 part, 0.35 part, 0.4 part, etc.

[0042] Some suitable wetting agents can be selected from at least one of polyether wetting agents, silicone and polyether mixture wetting agents, and alcohol alkoxylate wetting agents. Among them, polyether wetting agents can be, for example, fatty alcohol polyoxyethylene ether (lauryl alcohol polyoxyethylene ether, etc.), polyoxyethylene polyoxypropylene block copolymer (poloxamer, etc.), silicone and polyether mixture wetting agents can be, for example, the commercially available product Digo Wet 270, Evonik Wet 290, etc., and alcohol alkoxylate wetting agents can be, for example, isotridecanol polyoxyethylene ether, etc.

[0043] For any of the battery separators mentioned above, the maximum radial dimension of the glue dots parallel to the carrier layer can be 50 μm-1200 μm, the height of the glue dots can be 0.5 μm-10 μm, and the center distance between any two adjacent glue dots can be 300 μm-1200 μm.

[0044] By limiting the morphology of the glue points in the matrix glue layer, a gap is formed between the battery separator and the electrode, so that the battery separator has greater advantages in adhesion, liquid retention and air permeability. The matrix glue layer will not block the Li + channel, which can reduce the internal resistance of the battery and increase the cycle life of the battery.

[0045] Specifically, the maximum radial dimension of the glue dot along the direction parallel to the carrier layer is 50μm-1200μm, and can further be 100μm-1000μm, 200μm-800μm, 200μm-600μm, 200μm-500μm, etc. The radial dimension of the glue dot within the above range not only prevents the radial dimension of the glue dot from being too large, thereby allowing the glue dot to be evenly and densely distributed on the carrier layer, but also prevents the radial dimension of the glue dot from being too small, thereby allowing the matrix adhesive layer to provide sufficient bonding area. It should be noted that the maximum radial dimension of the glue dot along the direction parallel to the carrier layer can be considered as the dimension between the two points farthest apart among the multiple points corresponding to the edge of the glue dot in the orthographic projection on the carrier layer. For example, if the glue dot is spherical, the maximum radial dimension of the glue dot is its diameter. If the glue dot is rectangular, the radial dimension of the glue dot is its length. Methods for measuring the radial dimension of the glue dot include, but are not limited to, scanning electron microscopy (SEM), optical microscopy, and laser particle size analyzer.

[0046] The height of the glue dots is 0.5 μm-10 μm, and can further be 1 μm-10 μm, 1 μm-8 μm, 2 μm-8 μm, 2 μm-6 μm, 2 μm-5 μm, etc. The height of the glue dots is within the above range. On the one hand, the height of the glue dots is prevented from being too large, thereby ensuring the energy density of the manufactured battery separator. On the other hand, the particle size of the glue dots is prevented from being too small, thereby allowing the matrix glue layer to obtain a firm bonding effect and a desired liquid storage depth.

[0047] The center distance between any two adjacent glue dots is 300μm-1200μm, and can further be 300μm-1100μm, 300μm-1000μm, 300μm-900μm, 300μm-800μm, 500μm-1200μm, 500μm-1000μm, 500μm-800μm, etc. When the center distance between glue dots is within the above range, the resulting pore structure facilitates rapid electrolyte penetration and diffusion, while also retaining the electrolyte within the pores through capillary action, preventing electrolyte drying and loss, improving battery fluid retention, and extending battery life.

[0048] Furthermore, the amount of glue applied to the matrix glue layer on the surface of the carrier layer is 0.3 g / m 2 -1.5g / m 2The glue coating amount refers to the mass of the matrix glue layer per unit area, for example, it can be 0.5g / m 2 -1.5g / m 2 , 0.5g / m 2 -1.0g / m 2 wait.

[0049] The coverage of the matrix adhesive layer on the surface of the carrier layer is 20%-80%. Coverage refers to the percentage of the projected area of ​​the plurality of adhesive dots on the carrier layer surface to the carrier layer surface area. The coverage can be, for example, 30%-80%, 40%-80%, 50%-80%, and further can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc.

[0050] By limiting the amount of glue applied and the coverage of the glue layer as described above, the adhesion and liquid retention of the battery separator can be further optimized, and its air permeability increase can be reduced.

[0051] For any of the battery separators mentioned above, in some examples, the carrier layer includes at least a base film, which is a polyethylene base film (abbreviated as PE base film) or a polypropylene base film (abbreviated as PP base film). Both polyethylene base films and polypropylene base films have good chemical stability, high mechanical strength, excellent electrical insulation properties, suitable pore structure and pore size distribution, and are easy to process and shape, giving the battery separator excellent comprehensive performance.

[0052] It is not excluded that the carrier layer provided in embodiments of the present invention may further include: at least one of a nanofiber layer and a ceramic layer. For example, the carrier layer may include a base film and a nanofiber layer stacked in sequence, or a base film and a ceramic layer stacked in sequence, or a base film, a nanofiber layer, and a ceramic layer stacked in sequence. Accordingly, the matrix adhesive layer may be disposed on the surface of the nanofiber layer or the surface of the ceramic layer. The appropriate carrier layer can be selected based on actual needs.

[0053] In some examples, the base film satisfies at least one of the following parameters: a molecular weight of 300,000 g / mol-3,000,000 g / mol, including but not limited to: 500,000-2,000,000, 1,000,000-2,000,000, 1,500,000-2,000,000, etc.

[0054] When the base film has the above molecular weight range, it not only ensures that the base film has good mechanical strength, but also has good chemical stability.

[0055] The thickness of the base film is 1 μm-30 μm, including but not limited to 1 μm-10 μm, 5 μm-15 μm, 10 μm-20 μm, etc. When the thickness of the base film is within the above range, it is suitable for currently common types of secondary batteries.

[0056] The air permeability of the base film is 50s / 100ml-500s / 100ml, and can further be 100s / 100ml-300s / 100ml, 100s / 100ml-200s / 100ml, etc., to ensure that the battery separator has a suitable air permeability.

[0057] For the matrix adhesive layer involved in the embodiment of the present invention, the projection shape of its multiple adhesive points on the plane parallel to the carrier layer includes at least one of a circle, an ellipse, a square, and a polygon, wherein the polygon can be a regular polygon, which includes but is not limited to a regular pentagon, a regular hexagon, etc.

[0058] In summary, the battery separator provided by the embodiment of the present invention, by setting a matrix adhesive layer and improving the composition, morphology parameters and distribution of the matrix adhesive layer on the surface of the carrier layer, makes the battery separator exhibit excellent adhesion to both the positive and negative electrode sheets, and also exhibits excellent liquid retention performance and low air permeability increase, which is more beneficial to improving the cycle life of the battery.

[0059] In another aspect, embodiments of the present invention further provide a method for preparing a battery separator, as described above. The method comprises: providing a slurry comprising a matrix adhesive layer composition and water for forming a matrix adhesive layer; applying the slurry to both sides of a carrier layer using a matrix coating process; and curing the matrix adhesive layer to form a battery separator.

[0060] The composition of the adhesive layer composition can be found in the composition of the adhesive point described above. In some examples, the mass concentration of the adhesive layer composition in the slurry (i.e., the solid content of the slurry) can be 5%-35%, and further can be 5%-25%, with the solid content and the slurry formula being determined accordingly.

[0061] It should be noted that when the thickener in the adhesive layer composition is sodium hydroxymethyl cellulose, the sodium hydroxymethyl cellulose can be mixed with water to prepare an adhesive solution with a mass concentration of 0.5%-1.0%, and then mixed with other components to enhance the thickening effect.

[0062] In some examples, the slurry includes the following components in parts by weight: polymer: 8%-16%; dispersant 0.5%-1.5%; thickener 3%-9%; binder 2%-7%; wetting agent 0.1%-0.4%; and deionized water as the balance. The slurry can be used to prepare glue dots having the above composition.

[0063] In some examples, the slurry satisfies at least one of the following parameters: a viscosity of 30 mPa·s to 500 mPa·s, a particle size D50 of secondary particles in the slurry of ≤ 20 μm, and a particle size D90 of secondary particles in the slurry of ≤ 50 μm. The secondary particles in the slurry are obtained by agglomeration of polymer powder.

[0064] By combining the polymer powder particle size with the aforementioned limitations on the slurry's physical properties, the morphology of the glue dots can be effectively controlled, allowing for a particle size range of 50μm-1200μm, a height range of 0.5μm-10μm, and a center-to-center distance between any two adjacent glue dots of 300μm-1200μm. Furthermore, the amount of glue applied and the coverage of the matrix glue layer can be easily controlled.

[0065] In the embodiments of the present invention, some applicable matrix coating processes may include gravure coating, micro-gravure coating, transfer coating, spray coating, spin coating, etc. For example, transfer coating may be roller transfer application, which requires the use of a matrix application roller, which can be prepared by laser engraving.

[0066] In another aspect, embodiments of the present invention provide a thermal composite battery cell comprising a plurality of positive electrode sheets, a plurality of negative electrode sheets, and any of the aforementioned battery separators. The negative electrode sheets are stacked alternately with the positive electrode sheets, and adjacent negative electrode sheets are separated by a battery separator. The battery separator is bonded to the positive and negative electrode sheets via matrix adhesive layers on both sides.

[0067] The thermal composite battery cell provided by the embodiment of the present invention has all the advantages of the battery separator mentioned above.

[0068] In another aspect, an embodiment of the present invention provides a secondary battery, comprising: a housing, an electrolyte contained in the housing, and a thermal composite battery cell, wherein the thermal composite battery cell is as described above.

[0069] The secondary battery provided by the embodiment of the present invention has all the advantages of the battery separator mentioned above, which will not be described in detail here. For example, the secondary battery can be a lithium ion battery, a sodium ion battery, etc.

[0070] An embodiment of the present invention also relates to an electrical device, which includes the secondary battery involved above. For example, the electrical device can be a portable electronic device (mobile phone, laptop computer, smart wearable device, etc.), new energy transportation equipment (new energy vehicle, etc.), energy storage system, etc.

[0071] Below will be described in more detail exemplary embodiments of the present invention. Although the following describes exemplary embodiments of the present invention, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. In the examples, if specific techniques or conditions are not indicated, they are carried out according to the techniques or conditions described in the literature in this area or according to the product specifications. Reagents or instruments used that do not indicate the manufacturer are conventional products that can be obtained commercially.

[0072] Example 1

[0073] Example 1 provides a battery separator, which includes: a PE base film and a matrix adhesive layer stacked on both sides of the PE base film, the matrix adhesive layer includes a plurality of spherical adhesive dots, the adhesive dots have the following morphological parameters: the diameter of the adhesive dots is 600 μm, the height of the adhesive dots is 6 μm, and the center distance between any two adjacent adhesive dots is 750 μm, and the amount of adhesive applied to the surface of the carrier layer of the matrix adhesive layer is 1 g / m 2 , with a coverage rate of 50%.

[0074] The glue dots include the following components in parts by weight: 14 parts of polyvinylidene fluoride, 4 parts of polymethyl acrylate, 1 part of polyethylene glycol, 5 parts of sodium hydroxymethyl cellulose, and 0.2 parts of polyoxyethylene lauryl alcohol ether. The glass transition temperature of the polyvinylidene fluoride is -35°C ± 5°C, and the D50 value of the polyvinylidene fluoride is 7 μm.

[0075] The preparation method of the battery separator is as follows:

[0076] According to the composition of the glue dots, a glue layer composition is provided, wherein the thickener in the glue layer composition is sodium hydroxymethyl cellulose, which is mixed with water to form a glue solution with a mass concentration of 1.0%, and then the glue solution and other components in the glue layer composition are dissolved in water to form a slurry with a solid content of 20%.

[0077] A plate roller transfer application process is adopted, and the slurry is applied on one side of the carrier layer based on a matrix coating roller. After curing treatment, the slurry is applied on the other side of the carrier layer and the curing treatment is continued. Thus, a matrix adhesive layer is formed on both sides of the carrier layer to prepare the battery separator.

[0078] Example 2

[0079] Example 2 provides a battery separator, and the composition and preparation method of the battery separator can refer to Example 1.

[0080] The difference between Example 2 and Example 1 is that the composition of the glue dots is different. Specifically, the glue dots include the following components in parts by mass: 12 parts of hexafluoropropylene-modified polyvinylidene fluoride, 3 parts of polyethyl acrylate, 0.8 parts of polyvinyl alcohol, 7 parts of sodium hydroxymethyl cellulose, and 0.1 parts of lauryl alcohol polyoxyethylene ether.

[0081] The glass transition temperature of polyvinylidene fluoride is 70°C±5°C, and the particle size D50 of polyvinylidene fluoride is 10 μm.

[0082] Example 3

[0083] Example 3 provides a battery separator, and the composition and preparation method of the battery separator can refer to Example 1.

[0084] The difference between Example 3 and Example 1 is that the composition of the glue dots is different. Specifically, the glue dots include the following components in parts by weight: 13 parts of polymethyl methacrylate, 6 parts of polyethyl acrylate, 1.1 parts of sodium hexametaphosphate, 3 parts of sodium hydroxymethyl cellulose, and 0.3 parts of Evonik Wet 290.

[0085] The glass transition temperature of polymethyl methacrylate is 105° C.±5° C., and the particle size D50 of polymethyl methacrylate is 20 μm.

[0086] Example 4

[0087] Example 4 provides a battery separator, and the composition and preparation method of the battery separator can refer to Example 1.

[0088] Example 3 differs from Example 1 in that the adhesive dots have a different composition. Specifically, the adhesive dots include the following components in parts by weight: 16 parts polyvinylidene fluoride, 7 parts polyurethane-modified polyacrylate, 1.2 parts triethyl phosphate, 6 parts sodium hydroxymethyl cellulose, and 0.4 parts lauryl alcohol polyoxyethylene ether. The polyvinylidene fluoride has a particle size D50 of 15 μm.

[0089] Example 5

[0090] Example 5 provides a battery separator, and the composition and preparation method of the battery separator can refer to Example 1.

[0091] The difference between Example 5 and Example 1 is that the structural arrangement of the matrix adhesive layer is as follows: the morphological parameters of the adhesive dots are as follows: the diameter of the adhesive dots is 800 μm, the height of the adhesive dots is 3 μm, and the center distance between any two adjacent adhesive dots is 1200 μm. In addition, the amount of adhesive applied to the surface of the carrier layer by the matrix adhesive layer is 1 g / m 2 , with a coverage rate of 50%.

[0092] Example 6

[0093] Example 6 provides a battery separator, and the composition and preparation method of the battery separator can refer to Example 1.

[0094] The difference between Example 6 and Example 1 is that the structural arrangement of the matrix adhesive layer is as follows: the morphological parameters of the adhesive dots are as follows: the diameter of the adhesive dots is 200 μm, the height of the adhesive dots is 5 μm, and the center distance between any two adjacent adhesive dots is 250 μm. In addition, the amount of adhesive applied to the surface of the carrier layer by the matrix adhesive layer is 0.4 g / m 2 , with a coverage rate of 35%.

[0095] Example 7

[0096] Example 7 provides a battery separator, and the composition and preparation method of the battery separator can refer to Example 1.

[0097] The difference between Example 7 and Example 1 is that the structural arrangement of the matrix adhesive layer is as follows: the morphological parameters of the adhesive dots are as follows: the diameter of the adhesive dots is 400 μm, the height of the adhesive dots is 8 μm, and the center distance between any two adjacent adhesive dots is 500 μm. In addition, the amount of adhesive applied to the surface of the carrier layer by the matrix adhesive layer is 1.3 g / m 2 , with a coverage rate of 50%.

[0098] Comparative Example 1

[0099] Comparative Example 1 provides a battery separator having a base film surface fully coated with a glue layer. Specifically, the glue layer has a flat, layered structure with 100% coverage of the base film surface and a thickness of 6 μm. The glue layer formulation in Comparative Example 1 is the same as the glue point formulation in Example 1.

[0100] Comparative Example 2

[0101] Comparative Example 2 provides a battery separator, similarly provided with a matrix adhesive layer on the surface of the base film. The difference between Comparative Example 2 and Example 1 lies in the different adhesive dot formulation. The adhesive dot comprises the following components in parts by weight: 10 parts polyvinylidene fluoride, 6 parts acrylonitrile multi-polymer, and 3 parts styrene-maleic acid copolymer. The polyvinylidene fluoride has a D50 of 5 μm to 10 μm.

[0102] Test Case

[0103] The following performance tests were performed on the battery separators provided in Examples 1 to 7 and Comparative Examples 1 and 2. The test results are shown in Table 1.

[0104] (1) Adhesion strength: For the same batch of battery separators, the adhesion strength between the matrix adhesive layer and the base film in the battery separator is measured. The battery separator is bonded to a pole piece sample, and the adhesion strength between the pole piece sample and the battery separator is measured. The unit of adhesion strength is N / m.

[0105] (2) Liquid absorption: The battery separator was placed in an electrolyte solution (1 M LiPF6 electrolyte of vinyl carbonate (EC) and dimethyl carbonate (DMC) (v / v = 1:1)) for 1 h. After taking it out, the excess electrolyte solution was quickly washed out with filter paper. The mass change of the separator before and after adsorption was tested, and the liquid absorption percentage was calculated, with the unit being 100%.

[0106] (3) Air permeability: The test method for air permeability is carried out in accordance with GB / T458-2008, and the air permeability of the base film and the battery separator (base film + coating) at room temperature is measured respectively. The air permeability increment is the air permeability value of the battery separator minus the air permeability value of the base film. The unit of the air permeability value is s / 100mL.

[0107] (4) Battery internal resistance and cycle life: Lithium-ion batteries of the same specifications were prepared using the above-mentioned battery separators. The internal resistance and cycle life of the lithium-ion batteries were tested. The unit of internal resistance is mΩ, and the unit of cycle life is weeks. Each completed charge and discharge cycle is counted as one week.

[0108] Table 1

[0109]

[0110] As shown in Table 1, because Examples 1-7 provide a matrix adhesive layer comprising multiple raised adhesive dots on the surface of the base film, and because the composition of the adhesive dots has been improved, the matrix adhesive layer exhibits excellent adhesion and liquid absorption and retention. Furthermore, the matrix coating formed on the surface of the base film also exhibits a low air permeability increment (controlled to be less than or equal to 60 s / 100 mL). When the battery separators provided by Examples 1-7 are used in lithium-ion batteries, they effectively reduce the battery's internal resistance (less than 1 mΩ) and increase the battery's cycle life (greater than 3,000 cycles).

[0111] Comparative Example 1 uses a full-coating adhesive layer, and its bonding strength, liquid absorption, and air permeability increase are significantly deteriorated compared with Example 1, which in turn affects its application in lithium-ion batteries and is not conducive to reducing the battery's internal resistance and improving the cycle life.

[0112] Although Comparative Example 2 uses a matrix adhesive layer, the formula of its adhesive layer is different from that of the embodiment of the present invention, so that its bonding strength, liquid absorption and air permeability increase are slightly deteriorated compared with Example 1, which also affects its application in lithium-ion batteries and is not conducive to reducing the internal resistance of the battery and improving the cycle life.

[0113] The above description is only for the purpose of facilitating those skilled in the art to understand the technical solution of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A battery separator, characterized in that: The battery separator comprises: a carrier layer and a matrix adhesive layer stacked on both sides of the carrier layer, wherein the matrix adhesive layer comprises a plurality of adhesive dots distributed in a matrix and arranged in a raised manner; The glue dots include the following components in parts by weight: 8-16 parts of polymer, 2-7 parts of binder, 0.5-1.5 parts of dispersant, 3-9 parts of thickener, and 0.1-0.4 parts of wetting agent; The glass transition temperature of the polymer is -50°C to 110°C, and the particle size D50 of the polymer is 0.5 μm to 50 μm.

2. The battery separator according to claim 1, characterized in that The polymer is selected from at least one of polyvinylidene fluoride, hexafluoropropylene-modified polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyethylene-co-vinyl acetate, polyimide, and polyethylene oxide.

3. The battery separator according to claim 1, characterized in that The binder is selected from at least one of polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, silicone-modified polyacrylate, polyurethane-modified polyacrylate, and methacryloyl epoxy ester.

4. The battery separator according to claim 1, characterized in that The dispersant is selected from at least one of sodium hexametaphosphate, triethyl phosphate, sodium polyacrylate, ammonium polyacrylate, polyethylene glycol, polyvinyl alcohol, naphthalenesulfonic acid condensate, sodium cellulose sulfonate, and sodium lignin sulfonate.

5. The battery separator according to claim 1, characterized in that The thickener is selected from at least one of sodium hydroxymethyl cellulose and xanthan gum.

6. The battery separator according to claim 1, characterized in that The wetting agent is selected from at least one of polyether wetting agents, silicone and polyether mixture wetting agents, and alcohol alkoxylate wetting agents.

7. The battery separator according to any one of claims 1 to 6, characterized in that: The maximum radial dimension of the glue dots in a direction parallel to the carrier layer is 50 μm-1200 μm, the height of the glue dots is 0.5 μm-10 μm, and the center distance between any two adjacent glue dots is 300 μm-1200 μm.

8. The battery separator according to claim 7, characterized in that The coating amount of the matrix adhesive layer on the surface of the carrier layer is 0.3g / m 2 -1.5g / m 2 The coverage rate of the matrix adhesive layer on the surface of the carrier layer is 20%-80%.

9. The battery separator according to any one of claims 1 to 8, characterized in that: The carrier layer includes a base film, and the base film is a polyethylene base film or a polypropylene base film.

10. The battery separator according to claim 9, characterized in that The base film satisfies at least one of the following parameters: a molecular weight of 300,000 g / mol to 3,000,000 g / mol; a thickness of 1 μm to 30 μm; and an air permeability of 50 s / 100 ml to 500 s / 100 ml.

11. The battery separator according to claim 1, characterized in that The projected shapes of the plurality of glue dots on a plane parallel to the carrier layer include at least one of a circle, an ellipse, a square, and a polygon.

12. A method for preparing a battery separator, characterized in that: The battery separator according to any one of claims 1 to 11, wherein the preparation method comprises: Providing a slurry comprising a glue layer composition for forming a matrix glue layer and water; The slurry is applied on both sides of the carrier layer by a matrix coating process, and after curing, a matrix adhesive layer is formed on both sides of the carrier layer to prepare the battery separator.

13. A thermal composite battery cell, characterized in that: The thermal composite battery cell comprises a plurality of positive electrode sheets, a plurality of negative electrode sheets, and a battery separator according to any one of claims 1 to 11; The negative electrode sheets and the positive electrode sheets are alternately stacked, and the adjacent negative electrode sheets are separated from the positive electrode sheets by the battery separator, and the battery separator is respectively bonded to the positive electrode sheet and the negative electrode sheet through matrix adhesive layers on both sides.

14. A secondary battery, characterized in that: The secondary battery comprises: a shell, an electrolyte contained in the shell, and a thermal composite battery cell, wherein the thermal composite battery cell is as described in claim 13 .

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